1. Field of Invention
Aspects and embodiments of the present invention are directed to treatment of air streams, and more particularly, to systems and methods for removing odor causing compounds from an air stream.
2. Discussion of Related Art
Sewage systems typically include conduits that collect and direct sewage and other waste streams, such as industrial effluents, to a treatment facility. Such systems typically include various pumping facilities, such as lift stations, that facilitate the transfer of wastewater to such treatment facilities. During transit odorous species are often generated. Such odorous species may be objectionable when released or discharged. Untreated sewage may generate multiple odor-causing compounds. One of the most prevalent and most distinctive compounds formed is hydrogen sulfide (H2S).
Hydrogen sulfide may be formed in wastewater streams by the conversion of sulfates to sulfides by sulfide reducing bacteria (SRBs) under anaerobic conditions. Hydrogen sulfide is dissolvable in water (up to about 0.4 g/100 ml at 20 degrees Celsius and 1 atmosphere of pressure). In water, hydrogen sulfide exists in equilibrium with the bisulfide ion HS− and the sulfide ion S2−. Unlike sulfide and bisulfide, hydrogen sulfide is volatile, with a vapor pressure of about 1.56×104 mm Hg (2.1 MPa) at 25 degrees Celsius, and may emerge from aqueous solution to form gaseous hydrogen sulfide. The presence of hydrogen sulfide in sewer systems is undesirable due to its offensive odor, toxicity, and corrosivity.
Gaseous hydrogen sulfide exhibits a characteristic unpleasant odor suggestive of rotten eggs. Humans can detect this odor at hydrogen sulfide concentrations as low as four parts per billon (ppb). Hydrogen sulfide is considered toxic. The United States Occupational Safety and Health Administration (OSHA) has established a permissible exposure limit to hydrogen sulfide (8 hour time-weighted average) of 10 ppm. Extended exposure to a few hundred ppm can cause unconsciousness and death. Accordingly, the presence of hydrogen sulfide in sewer systems is found objectionable to people who may come into contact with the gaseous effluent from such sewer systems.
Hydrogen sulfide also supports the growth of organisms such as thiothrix and beggiatoa. These are filamentous organisms which are associated with bulking problems in activated sludge treatment systems.